The present invention relates generally to method and apparatus for processing logs in a sawmill and in particular to such a method and apparatus in which the logs are rotationally repositioned in an end dogging carriage to a desired cutting position after they are scanned in a non-rotational light scanner to determine the configuration of the log and the scan data is fed to a computer to determine the proper cutting pattern for the log. The log is transferred from the scanner to the carriage and then rotationally repositioned by means of a rotationally driven end dog blade engaging one end of the log to rotate it about the axis of a selected chuck which is extended from the end dog at the other end of such log. After the log is rotationally repositioned to the proper cutting position additional end dog chucks are extended into contact with such log to prevent further rotation while the carriage transports the log through the cutting devices, including a bottom chipper head which may be adjusted vertically to provide a curved or straight bottom surface to the log. As a result of such rotational repositioning of the log before cutting, the lumber yield from the log is increased significantly.
It has been previously proposed in U.S. Pat. No. 4,947,909 to Stroud, issued Aug. 14, 1990, to provide a log processing apparatus for a sawmill in which the log is scanned with a non-rotational scanner by transporting the log on a spiked chain conveyor longitudinally through such scanner. The scanner output signal data is fed to a computer which processes such data to determine the configuration of the log and controls the cutting devices, including a top cutting head which is adjusted vertically to provide a top surface which is curved or straight. However, this apparatus has the disadvantage that the log is fixed to the conveyor by the spikes embedded in the bottom of the log so the log cannot be rotationally repositioned to a desired cutting position after it is scanned and transferred to the conveyor, unlike the present invention. Also, the spiked conveyor chain does not hold the log in position as securely as the end dogging carriage and there is no room for a bottom chipping head because of the spikes which may also block the scanner beams. Finally the scanner is slower than the present invention because the log is scanned longitudinally, not laterally.
It has been previously disclosed in U.S. Pat. No. 4,152,960 to Detjen, issued May 8, 1979, to provide a sawmill apparatus having an end dogging carriage for transporting the logs through the sawmills while they are engaged by a pusher dog and a hold-back dog. Prior to engagement by the end dogs, the log is scanned and rotationally oriented to the desired log orientation. However, the log is not rotationally repositioned to the desired cutting position after transfer to the carriage by a rotationally driven end dog blade and a selectable end dog chuck in the manner of the present invention. Thus by transfer of the log to the end dogging carriage after it is repositioned, in the Detjen apparatus the rotational orientation of the log may be accidentally changed during transfer. In addition, there is no mention of laser light scanning or computer processing of the scanning signal in the manner of the present invention.
U.S. Pat. No. 4,867,213 to Bolton et al., issued Sep. 19, 1989, shows a log processing apparatus for a sawmill in which the log is scanned while it is rotated on spindles in a log charger. The scanning spindles at the opposite ends of the log are adjusted in an X-Y direction for angular adjustment or "skewing" of the log axis to the desired cutting position before the log is transferred to the overhead log carriage for conveying the log through the saws and other cutting devices. This has the disadvantage that the rotational orientation and angular skew position of the log may be accidentally changed during transfer so that the log is no longer in the desired cutting position when conveyed by the carriage. Thus, the Bolton apparatus is slower and less accurate and is more complicated and expensive than the method and apparatus of the present invention because in the latter the log is rotationally repositioned to the desired cutting position after transfer to the end dogging carriage. In addition with the present invention the repositioning is by rotating the end dogs under control of the computer in accordance with the desired cutting solution determined from the scanning signal data produced by light scanning of the log in the log charger before transfer to the carriage. Also, the log is more rapidly scanned by moving it laterally with the charger arms through a non-rotational scanner.
U.S. Pat. No. 4,996,900 to Schmidt et al., issued Mar. 5, 1991, shows an end dogging sawmill carriage with independent cable drives for the two end dogs in which the two drive cables are releaseably coupled together by an automatic clamp to temporarily provide a common drive for the two end dogs to move the log through the cutting devices but to otherwise allow them to be driven independently of each other. A similar end dogging carriage is used for the present invention. However, unlike the present invention, this patent does not disclose the use of rotationally driven blade on one end dog or the use of a plurality of selective extendable chucks on the other end dog in order to allow the log to be rotationally repositioned to the proper cutting position after transfer from the scanner to the carriage.
U.S. Pat. No. 4,803,371 of Durland, issued Feb. 7, 1989, discloses an optical scanning method and apparatus for scanning a log to determine its configuration with a plurality of laser light beams spaced along the log and a plurality of polychromatic light sources which are directed to the log and are detected by photo-detector cameras. This prior system is employed to scan elongated objects, including logs and unfinished lumber such as cants, to determine the configuration of such lumber for optimizing the size and number of boards which can be cut from such lumber using a computer which processes the scan data signals produced by the photo-detector cameras.